ALSA: timer: Limit max instances per timer
Currently we allow unlimited number of timer instances, and it may
bring the system hogging way too much CPU when too many timer
instances are opened and processed concurrently. This may end up with
a soft-lockup report as triggered by syzkaller, especially when
hrtimer backend is deployed.
Since such insane number of instances aren't demanded by the normal
use case of ALSA sequencer and it merely opens a risk only for abuse,
this patch introduces the upper limit for the number of instances per
timer backend. As default, it's set to 1000, but for the fine-grained
timer like hrtimer, it's set to 100.
Reported-by: syzbot
Tested-by: Jérôme Glisse <jglisse@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/include/sound/timer.h b/include/sound/timer.h
index c4d76ff..7ae226a 100644
--- a/include/sound/timer.h
+++ b/include/sound/timer.h
@@ -90,6 +90,8 @@
struct list_head ack_list_head;
struct list_head sack_list_head; /* slow ack list head */
struct tasklet_struct task_queue;
+ int max_instances; /* upper limit of timer instances */
+ int num_instances; /* current number of timer instances */
};
struct snd_timer_instance {
diff --git a/sound/core/hrtimer.c b/sound/core/hrtimer.c
index 1ac0c42..6e47b82 100644
--- a/sound/core/hrtimer.c
+++ b/sound/core/hrtimer.c
@@ -159,6 +159,7 @@
timer->hw = hrtimer_hw;
timer->hw.resolution = resolution;
timer->hw.ticks = NANO_SEC / resolution;
+ timer->max_instances = 100; /* lower the limit */
err = snd_timer_global_register(timer);
if (err < 0) {
diff --git a/sound/core/timer.c b/sound/core/timer.c
index 6cdd04a..15e82a6 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -180,7 +180,7 @@
*
* call this with register_mutex down.
*/
-static void snd_timer_check_slave(struct snd_timer_instance *slave)
+static int snd_timer_check_slave(struct snd_timer_instance *slave)
{
struct snd_timer *timer;
struct snd_timer_instance *master;
@@ -190,16 +190,21 @@
list_for_each_entry(master, &timer->open_list_head, open_list) {
if (slave->slave_class == master->slave_class &&
slave->slave_id == master->slave_id) {
+ if (master->timer->num_instances >=
+ master->timer->max_instances)
+ return -EBUSY;
list_move_tail(&slave->open_list,
&master->slave_list_head);
+ master->timer->num_instances++;
spin_lock_irq(&slave_active_lock);
slave->master = master;
slave->timer = master->timer;
spin_unlock_irq(&slave_active_lock);
- return;
+ return 0;
}
}
}
+ return 0;
}
/*
@@ -208,7 +213,7 @@
*
* call this with register_mutex down.
*/
-static void snd_timer_check_master(struct snd_timer_instance *master)
+static int snd_timer_check_master(struct snd_timer_instance *master)
{
struct snd_timer_instance *slave, *tmp;
@@ -216,7 +221,11 @@
list_for_each_entry_safe(slave, tmp, &snd_timer_slave_list, open_list) {
if (slave->slave_class == master->slave_class &&
slave->slave_id == master->slave_id) {
+ if (master->timer->num_instances >=
+ master->timer->max_instances)
+ return -EBUSY;
list_move_tail(&slave->open_list, &master->slave_list_head);
+ master->timer->num_instances++;
spin_lock_irq(&slave_active_lock);
spin_lock(&master->timer->lock);
slave->master = master;
@@ -228,8 +237,11 @@
spin_unlock_irq(&slave_active_lock);
}
}
+ return 0;
}
+static int snd_timer_close_locked(struct snd_timer_instance *timeri);
+
/*
* open a timer instance
* when opening a master, the slave id must be here given.
@@ -240,6 +252,7 @@
{
struct snd_timer *timer;
struct snd_timer_instance *timeri = NULL;
+ int err;
if (tid->dev_class == SNDRV_TIMER_CLASS_SLAVE) {
/* open a slave instance */
@@ -259,10 +272,14 @@
timeri->slave_id = tid->device;
timeri->flags |= SNDRV_TIMER_IFLG_SLAVE;
list_add_tail(&timeri->open_list, &snd_timer_slave_list);
- snd_timer_check_slave(timeri);
+ err = snd_timer_check_slave(timeri);
+ if (err < 0) {
+ snd_timer_close_locked(timeri);
+ timeri = NULL;
+ }
mutex_unlock(®ister_mutex);
*ti = timeri;
- return 0;
+ return err;
}
/* open a master instance */
@@ -288,6 +305,10 @@
return -EBUSY;
}
}
+ if (timer->num_instances >= timer->max_instances) {
+ mutex_unlock(®ister_mutex);
+ return -EBUSY;
+ }
timeri = snd_timer_instance_new(owner, timer);
if (!timeri) {
mutex_unlock(®ister_mutex);
@@ -314,25 +335,27 @@
}
list_add_tail(&timeri->open_list, &timer->open_list_head);
- snd_timer_check_master(timeri);
+ timer->num_instances++;
+ err = snd_timer_check_master(timeri);
+ if (err < 0) {
+ snd_timer_close_locked(timeri);
+ timeri = NULL;
+ }
mutex_unlock(®ister_mutex);
*ti = timeri;
- return 0;
+ return err;
}
EXPORT_SYMBOL(snd_timer_open);
/*
* close a timer instance
+ * call this with register_mutex down.
*/
-int snd_timer_close(struct snd_timer_instance *timeri)
+static int snd_timer_close_locked(struct snd_timer_instance *timeri)
{
struct snd_timer *timer = NULL;
struct snd_timer_instance *slave, *tmp;
- if (snd_BUG_ON(!timeri))
- return -ENXIO;
-
- mutex_lock(®ister_mutex);
list_del(&timeri->open_list);
/* force to stop the timer */
@@ -340,6 +363,7 @@
timer = timeri->timer;
if (timer) {
+ timer->num_instances--;
/* wait, until the active callback is finished */
spin_lock_irq(&timer->lock);
while (timeri->flags & SNDRV_TIMER_IFLG_CALLBACK) {
@@ -355,6 +379,7 @@
list_for_each_entry_safe(slave, tmp, &timeri->slave_list_head,
open_list) {
list_move_tail(&slave->open_list, &snd_timer_slave_list);
+ timer->num_instances--;
slave->master = NULL;
slave->timer = NULL;
list_del_init(&slave->ack_list);
@@ -382,9 +407,24 @@
module_put(timer->module);
}
- mutex_unlock(®ister_mutex);
return 0;
}
+
+/*
+ * close a timer instance
+ */
+int snd_timer_close(struct snd_timer_instance *timeri)
+{
+ int err;
+
+ if (snd_BUG_ON(!timeri))
+ return -ENXIO;
+
+ mutex_lock(®ister_mutex);
+ err = snd_timer_close_locked(timeri);
+ mutex_unlock(®ister_mutex);
+ return err;
+}
EXPORT_SYMBOL(snd_timer_close);
unsigned long snd_timer_resolution(struct snd_timer_instance *timeri)
@@ -856,6 +896,7 @@
spin_lock_init(&timer->lock);
tasklet_init(&timer->task_queue, snd_timer_tasklet,
(unsigned long)timer);
+ timer->max_instances = 1000; /* default limit per timer */
if (card != NULL) {
timer->module = card->module;
err = snd_device_new(card, SNDRV_DEV_TIMER, timer, &ops);
